Have you ever noticed that everyone has their own opinions of how venomous an animal is? When we watch TV, we see programs such as the 10 Most Deadly Animals In The World, or Snakes Of Death... and they list different animals in their top 10 most venomous? That's because measuring toxicity is not as easy as you think. There are different methods of measuring venom toxicity which have advantages and disadvantages. None of these methods can give us a clear idea of how venomous an animal is in comparison to other animals.
Venoms are a complex mixture of man different components, each responsible for an action of that venom. Venom is often selective which means it is often targeted towards a certain prey species of animal. In order to "measure" toxicity, we can use the following as a general guideline.
LD50 is short for Lethal Dose 50%. It’s an indication of the amount of venom necessary to kill 50% of the test animals injected by a venom. The amount is expressed as the weight of venom per 1kg of test animal body weight.
This test is often viewed as flawed since different animals react in different ways, resulting in unreliable results. Mice are often utilised as test animals because of the ethical concerns pertaining to larger animals.
Specific Toxicity Tests
Specific toxicity tests are a range of tests that have been developed to measure the toxicity of a venom under various specific circumstances or situations. These tests may involve live animals or tissue cultures.
Exposing tissue cultures to venom provide insight into how a venom effects aspects such as blood clotting, blood cell destruction, kidney damage, heart and muscle damage and neurotoxicity.
Specific toxicity tests do not provide comparative results, but rather indicate the action of the venom.
Number Of Deaths
This is probably the most inaccurate yardsticks to measure how venomous an animal is. There are so many factors that influence the outcome of an envenomation that the number of deaths is a very unreliable indicator. The Sydney Funnel Web Spider is a good example of this. According to LD50 tests, this spider (or at least the males) are highly venomous, yet the last death was in 1981. Only 12 deaths have ever been recorded is comparable to the number of Americas that are killed by vending machines falling onto them (14 deaths annually). In 1981, antivenom for this spider was developed, reducing the number of deaths to zero.
In areas where medical facilities are lacking, deaths from highly venomous creatures are common. In areas with medical facilities, the same creature is unlikely to cause any deaths.